Integrated circuits can be printed on semiconductor wafers by exposure tools in a photolithography process by irradiance of, e.g., deep ultra-violet (DUV) radiation through photomasks. As design rules of the complementary metal oxide semiconductor (CMOS) technology printed features become smaller, the role of aberrations that lead to wave-front phase errors on exposure tools and optical imaging systems become more significant. Smaller resolvable features, such as lines and spaces or contact holes, can be achieved by light sources with shorter wavelength (e.g., DUV) radiation and by an increase in numerical aperture (NA) of the projection optics. Increasing the numerical aperture of the projection optics may result in higher sensitivity to aberrations and phase errors of the wave-front at the pupil planes of optical systems.
Optical tools manufacturers may measure each tool's imaging optics for their aberrations distribution, and a map of wave-front phase errors can be generated. Such maps of phase errors can also be measured and constructed for individual lenses and groups of lenses. The optical surfaces can be precision polished and some of the phase errors can be corrected based on the phase error maps.